The speaker admits that when he was 21 years old, he wasn't that open to lessons or advices being given to him. But I was one-and-twenty, No use to talk to me. He doesn't listen to those of experience when he is being taught. Here we see that the speaker used the word "paid" to continue the imagery of currency and gems. There is always an exchange in life. You have to give something to get something. The speaker's monologue in a simply and clearly expressed agreement with the wise man's warnings. And I am twenty-two